RF power transfer efficiency and plasma parameters of low pressure high power ICPs

Zielke, D.; Briefi, S.; Fantz, U.

doi:10.1088/1361-6463/abd8ee

Cited by 33 publications

(45 citation statements)

References 24 publications

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“…Experimental data from discharges of the ITER prototype RF negative ion source is used for the validation of the model. Typical operation is at a low filling pressure of 0.3 Pa, a driving frequency of 1 MHz and at large RF powers up to 75 kW [6]. The numerically obtained solutions are compared to values which are experimentally obtained from the plasma production region (driver).…”

Section: Investigation Of Rf Power Coupling Mechanism In Rf Ion Sourcesmentioning

confidence: 99%

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Predictive fluid model for self-consistent description of inductive RF coupling in powerful negative hydrogen ion sources

Zielke

Briefi

Lishev

et al. 2022

J. Phys.: Conf. Ser.

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RF-driven negative hydrogen ion sources are typically operated at low frequencies around 1 MHz, gas pressures around or below 1 Pa and large power densities up to 10 Wcm-3. Owing to these conditions as well as the current discharge geometries and antenna layouts, the RF power coupling is far from optimized, i.e. only a fraction η of the power delivered by the generator is absorbed by the plasma. This considerably limits the performance and reliability of RF-driven ion sources. To study the bidirectional RF power coupling a self-consistent fluid model is introduced. Taking into account the interplay between the nonlinear RF Lorentz force and the electron viscosity (usually neglected in state-of-the-art fluid models) a steady state solution is obtained, where the trends reflect the experimental data. Solutions calculated in hydrogen but with increased ion masses indicate that the latter are responsible for the systematically increased η, which is observed experimentally when deuterium instead of hydrogen is used as feed gas.

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Section: Investigation Of Rf Power Coupling Mechanism In Rf Ion Sourcesmentioning

confidence: 99%

“…Optimizing the RF power coupling in inductively driven radio frequency (RF) ion sources is a worthwhile task, since it can lead to significant improvement of the RF power transfer efficiency [1][2][3][4][5][6]…”

Section: Introductionmentioning

confidence: 99%

Predictive fluid model for self-consistent description of inductive RF coupling in powerful negative hydrogen ion sources

Zielke

Briefi

Lishev

et al. 2022

J. Phys.: Conf. Ser.

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“…In order to assess the RF power transfer efficiency for RFdriven H − ion sources fundamentally, a detailed experimental investigation has been carried out at BUG [22]. As the DC insulating transformer is specific for the electrical structure of the testbeds and not applied at the ITER sources (where the RF generators are also set at high voltage), the measurements were carried out without the transformer.…”

Section: Coupling Efficiencymentioning

confidence: 99%

“…The lines of sight are arranged such that one measures axially through the driver; two others are vertically centered and measure in horizontal direction FIGURE 2 | RF power transfer efficiency at BUG for varying generator power P gen (A) and electron density obtained from Langmuir probe measurements in the driver center plotted as a function of the power absorbed by the plasma P plasma (B). The figure is adapted from [22]. at a distance of 18 cm (labeled expansion) and at 2.6 cm (labeled PG) upstream of the extraction system.…”

Section: Plasma Parametersmentioning

confidence: 99%

Negative Hydrogen Ion Sources for Fusion: From Plasma Generation to Beam Properties

et al. 2021

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The neutral beam injection systems for the international fusion experiment ITER used for heating, current drive, and diagnostic purposes are based on RF-driven negative hydrogen ion sources with a source area of roughly 0.9 m × 1.9 m. The sources operate at 0.3 Pa in hydrogen and in deuterium using a total available RF generator power of 800 kW per source at a frequency of 1 MHz. In order to fulfill the challenging requirements for ITER and beyond (like a DEMOnstration power plant, DEMO), worldwide developments are underway addressing the topics of plasma generation, ion extraction together with the issue of reducing and stabilizing the co-extracted electron current, and the beam properties. At the example of the activities at the ITER prototype source and the size scaling experiment ELISE, the present status and its challenges are summarized. The RF power transfer efficiency of these sources is only about 65% in maximum, giving significant room for improvements to relax the demands on the RF generator and ensure reliable operation. The plasma uniformity in front of the large extraction system is the result of plasma drifts. They have a huge impact on the nonuniformity of the co-extracted electrons and influence the ions and thus the beam properties as well. Understanding the optics of such large beams composed of hundreds of beamlets is a crucial task and is under continuous improvement. The main challenge, however, is still the fulfillment of the ITER requirements for deuterium, in particular, for long pulses. The management of caesium, which is evaporated into the source to generate sufficient negative ions by the surface conversion process, is one of the keys for stable and reliable operation.

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“…However, the RF power transfer efficiency is influenced in a non-trivial way by many operational and design parameters such as gas pressure, RF power level, driving frequency, and source geometry. A dedicated measurement campaign at the BATMAN Upgrade test bed revealed, that η is only in the range between 50 and 60% for typical operational conditions of NBI H − ion sources providing a substantial optimization potential [8].…”

Section: Introductionmentioning

confidence: 99%

RF power transfer efficiency of H ion sources: fluid modeling of accelerator source geometries

Briefi

Zielke

Fantz

2022

J. Phys.: Conf. Ser.

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The plasma in RF driven negative hydrogen ion sources is sustained via inductive coupling with large power levels of up to 100 kW and low frequencies around 1 MHz. This leads to currents of around 100 A flowing over the RF coil and corresponding voltages in the kV range. The associated risk of arcing limits the reliability of the whole ion source. The required power level can be reduced via optimizing the RF power transfer efficiency η, which is typically only in the range of 50 to 60% for H- sources used for neutral beam injection systems. In order to study the optimization of η systematically, a self-consistent fluid model has been set up and successfully validated with experimental measurements at the BATMAN Upgrade test bed. For H- sources applied at particle accelerators, no experimental measurements of η are available so far. In order to gain a first insight into the RF power transfer efficiency of these sources, exemplary simulations were carried out with the fluid code. The simulated plasma parameters are in good agreement with results from OES measurements. η shows an increasing trend with larger source radius and a virtually constant value with increasing RF power. For benchmarking these first results, dedicated measurements at an accelerator source setup are inevitable.

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RF power transfer efficiency and plasma parameters of low pressure high power ICPs

Cited by 33 publications

References 24 publications

Predictive fluid model for self-consistent description of inductive RF coupling in powerful negative hydrogen ion sources

Predictive fluid model for self-consistent description of inductive RF coupling in powerful negative hydrogen ion sources

Negative Hydrogen Ion Sources for Fusion: From Plasma Generation to Beam Properties

RF power transfer efficiency of H ion sources: fluid modeling of accelerator source geometries

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